The present invention relates in general to a compressor and more particularly to a swash plate type compressor.
A swash plate type compressor has a swash plate rotatably connected with a rotational shaft, a reciprocally movable piston, and a piston joint connecting the swash plate with the piston. The piston joint, for example, has a shoe which has a plain surface slidable along the swash plate and a convex curved surface on the opposite side of the plain surface, and a socket which has a concave spherical surface for receiving the projecting, convex curved surface of the piston, as shown for example in Japanese Unexamined Publications Nos. 61-135990, 49-65509, and 56-138474.
In the operational mode of the compressor, the shoe moves within the socket of the piston to have a wobbling motion in accordance with a rotational movement of the swash plate. Thus, it is strongly desired to maintain a favorable lubricating efficiency between the convex curved surface of the shoe and the concave spherical surface of the socket.
For example, U.S. Pat. No. 4,734,014 shows a structure in which a convex portion of the shoe is formed to have smaller radius curvature than a curvature of a concave portion of the socket and a top of the concave spherical curved surface is provided with a plain surface. In this structure, an oil reservoir is formed between the plain surface of the shoe and the recess or concave portion of the socket to provide a desirable lubricity or a lubricant characteristic. Here, a position where the shoe contacts with the concave portion of the socket is located adjacent to the oil reservoir. Namely, an angular portion located at a border between the spherical curved surface of the shoe and the plain surface is contacted with the concave portion of the socket.
In general, there are some clearances or gaps between the concave portion of the socket and the convex or projecting portion of the shoe and between the plain surface of the shoe and the swash plate and, therefore, a relative vibration is produced in the axial direction of the compressor in an operation of the compressor and, a relative vibration is produced in the direction perpendicular to the axial direction. As a result of the relative vibrations and the wobbling motion as described above, it is foreseen that a special condition is generated that the border portion of the shoe contacts the concave portion of the socket, at a limited position of a portion or a point of the circumferential portion of the oil reservoir.
When such a special condition as described above occurs, a reaction of the compression by the reciprocal movement of the piston is concentrated on a part or point of its contacted area. Accordingly, in the conventional shoe structure in which an angular portion is contacted with the concave spherical surface of the socket, it is likely that the concave portion of the socket is deformed due to plastic deformation, plastic flow and/or frictional wear. Consequently, there is a problem that the relative vibrations are likely to be generated.